Vinegar is fine long as you rinse really thoroughly after. I use it on my hands a lot of times when I've been wearing perfume on my clothes and can smell it on my hands, or handling soap or just gotten done washing my hair, etc. and am not satisfied with the results of a thorough water washing. it's acidic, which is probably /why/ it works, so just be sure to rinse, scrub with a paper towel, rinse, and repeat a good few times. ^-^
and like Pew said, a tiny bit of vinegar is much less harmful than a tiny bit of bleach ^-^

please try the salt method first, before trying any more medicines, as the more natural and more mild the treatment can be, the better for you and your little fishy. D:

also you didn't tell us how often you change the water? ^-^;

in a filtered 1.5 I /think/ it needs a water change every day or every other, but my smallest is a 2.5 and it's unfiltered, so I'm not positive. ><
I prefer 50% changes so I don't have to move my fish, but a 1.5 may be too small for those, and I know for some fish, dependent on personality, they'd just rather be moved, than have to deal with your hand and all the water movement ^-^;